This invention relates to a method for forming heated glass sheets.
Glass sheet forming systems conventionally include a furnace having a heating chamber in which a conveyor conveys glass sheets for heating to a sufficiently hot temperature to permit forming. Normally furnace heating chambers are heated to about 650 to 720xc2x0 C. to provide glass sheet heating to about 620 to 660xc2x0 C. for forming by one or more molds and optional subsequent quenching. U.S. Pat. Nos. 4,578,103 Fackelman, U.S. Pat. No. 4,615,724 Fackelman and U.S. Pat. No. 5,002,599 McMaster et al. disclose topside transfer devices for transferring heated glass sheets without any direct contact from a heating conveyor to a mold for forming. A vacuum and pressurized air supplied to a downwardly facing surface of the topside transfer device provides the topside support of the glass sheet without any direct contact. Such transfer can be effectively performed by using positioning apparatus as disclosed by U.S. Pat. Nos. 5,066,321 Kramer et al., U.S. Pat. No. 5,669,953 Schnabel, Jr. et al., and U.S. Pat. No 5,902,366 Schnabel, Jr. et al. The forming has previously been performed with an upper mold also located within the heating chamber of the furnace as disclosed by U.S. Pat. No. 4,575,390 McMaster.
While glass sheet forming has previously been conducted externally of a furnace heating chamber as disclosed by U.S. Pat. No. 5,755,845 Woodward et al., the transfer of the glass sheet to such external molds has previously been performed by roller conveyors which require a split mold for passing through the molds to perform the forming. While use of external molds is desirable in allowing the use of materials that do not have to withstand the relatively high temperature of a furnace heating chamber, there has not heretofore been an effective system or method for performing glass sheet forming at an external location outside of the furnace heating chamber.
An object of the invention is to provide an improved method for forming glass sheets.
In carrying out the above object, the method for forming glass sheets in accordance with the invention is performed by conveying a glass sheet within a heating chamber of a furnace for heating sufficiently hot to permit forming of the glass sheet. The heated glass sheet is transferred to a downwardly facing surface of a topside transfer device within the heating chamber of the furnace where vacuum and pressurized air are supplied to support the heated glass sheet without any direct contact. The hot glass sheet is released from the topside transfer device onto a lower ring, and the lower ring is then moved with the hot glass sheet thereon horizontally out of the heating chamber of the furnace to a forming station that includes an upper mold located externally of the furnace heating chamber so the upper mold has a temperature that is not greater than 500xc2x0 C. The upper mold of the forming station is then moved downwardly to cooperate with the lower ring in forming the hot glass sheet.
In carrying out the glass sheet forming method, heat loss of the hot glass sheet is reduced during the forming.
The forming method is also performed utilizing an impulse vacuum that is supplied to the upper mold to assist in the glass sheet forming.
The glass sheet forming method is also disclosed as including moving the formed glass sheet horizontally from the forming station to a cooling station for cooling which may be annealing, heat strengthening or tempering.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.